1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more specifically, to technology in which problems of devices generated when a polysilicon film is patterned using a nitride film as a hard mask can be solved.
2. Discussion of Related Art
Generally, in the process of manufacturing a semiconductor device, a minute pattern is formed using a photoresist film. As the aspect ratio of the pattern becomes large and the level of integration increases, however, there is a problem in that patterning becomes difficult with only the photoresist film. Therefore, patterning is performed using a film having an etch ratio that is higher than an underlying film to be patterned as a hard mask film. That is, in order to pattern a polysilicon film or an oxide film, the nitride film is used as the hard mask film.
A polysilicon film or an oxide film is deposited on a semiconductor substrate and a nitride film is then deposited. After the nitride film is patterned, an etching process using the nitride film as an etch mask is performed to pattern the polysilicon film or the oxide film. A nitride film removal process is performed to remove the nitride film. The polysilicon film or the oxide film is thus patterned.
In the conventional nitride film removal process, a phosphoric acid dip-out process is employed in which the nitride film is removed by dipping the semiconductor substrate into a phosphor acid aqueous solution of a high temperature. During the phosphoric acid dip-out process, however, an abnormal oxide film is formed on the nitride film. Thus, there is a problem in that the nitride film is not fully removed. In the case where an excessive nitride film removal process is performed in order to solve this problem, this leads to damage of an underlying pattern. For this reason, it has a great influence upon patterns such as a polysilicon film formed at the bottom.